Namespace error occuring on validated file

I'm having the lot of XSD, which is included with single XSD file and all the files are getting valid well and the corresponding XML file also getting valid against corresponding XSD using oxygen XML editor. But while uploading the xml file against the XSD's file in the product. I'm getting the below error:

    Error resolving component 'Definition.attrib'. It was detected that 'Definition.attrib' has no namespace, but components with no target namespace are not referenceable from schema document

When I opened the corresponding file, it shows validated in oxygen XML editor. Here is the code for the corresponding file:

<?xml version="1.0" encoding="UTF-8"?>

<xs:schema 
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns="http://www.w3.org/1998/Math/MathML"
  targetNamespace="http://www.w3.org/1998/Math/MathML"
  elementFormDefault="qualified"
 >

<xs:include schemaLocation="common-attrib.xsd"></xs:include>
<xs:include schemaLocation="../common/common-attribs.xsd"></xs:include>

<xs:attributeGroup name="mean.attlist">
  <xs:attributeGroup ref="Definition.attrib"/>
  <xs:attributeGroup ref="Common.attrib"/>
</xs:attributeGroup>


<xs:complexType name="mean.type">
  <xs:attributeGroup ref="mean.attlist"/>
</xs:complexType>

<xs:element name="mean" type="mean.type"/>

<xs:attributeGroup name="sdev.attlist">
  <xs:attributeGroup ref="Definition.attrib"/>
  <xs:attributeGroup ref="Common.attrib"/>
</xs:attributeGroup>

<xs:complexType name="sdev.type">
  <xs:attributeGroup ref="sdev.attlist"/>
</xs:complexType>

<xs:element name="sdev" type="sdev.type"/>

<!-- "variance" -->

<xs:attributeGroup name="variance.attlist">
  <xs:attributeGroup ref="Definition.attrib"/>
  <xs:attributeGroup ref="Common.attrib"/>
</xs:attributeGroup>

<xs:complexType name="variance.type">
  <xs:attributeGroup ref="variance.attlist"/>
</xs:complexType>

<xs:element name="variance" type="variance.type"/>

<!-- "median" -->

<xs:attributeGroup name="median.attlist">
  <xs:attributeGroup ref="Definition.attrib"/>
  <xs:attributeGroup ref="Common.attrib"/>
</xs:attributeGroup>

<xs:complexType name="median.type">
  <xs:attributeGroup ref="median.attlist"/>
</xs:complexType>

<xs:element name="median" type="median.type"/>

<!-- "mode" -->

<xs:attributeGroup name="mode.attlist">
  <xs:attributeGroup ref="Definition.attrib"/>
  <xs:attributeGroup ref="Common.attrib"/>
</xs:attributeGroup>

<xs:complexType name="mode.type">
  <xs:attributeGroup ref="mode.attlist"/>
</xs:complexType>

<xs:element name="mode" type="mode.type"/>

<!-- "moment" -->

<xs:attributeGroup name="moment.attlist">
  <xs:attributeGroup ref="Definition.attrib"/>
  <xs:attributeGroup ref="Common.attrib"/>
</xs:attributeGroup>

<xs:complexType name="moment.type">
  <xs:attributeGroup ref="moment.attlist"/>
</xs:complexType>

<xs:element name="moment" type="moment.type"/>

<!-- "momentabout" -->

<xs:attributeGroup name="momentabout.attlist">
  <xs:attributeGroup ref="Definition.attrib"/>
  <xs:attributeGroup ref="Common.attrib"/>
</xs:attributeGroup>

<xs:group name="momentabout.content">
  <xs:sequence>
    <xs:group ref="Content-statistics.class"/>
  </xs:sequence>
</xs:group>

<xs:complexType name="momentabout.type">
  <xs:group ref="momentabout.content"  minOccurs="1" maxOccurs="unbounded"/>
  <xs:attributeGroup ref="momentabout.attlist"/>
</xs:complexType>

<xs:element name="momentabout" type="momentabout.type"/>

<!-- And the group of everything -->

<xs:group name="Content-statistics.class">
  <xs:choice>
    <xs:element ref="mean"/>
    <xs:element ref="sdev"/>
    <xs:element ref="variance"/>
    <xs:element ref="median"/>
    <xs:element ref="mode"/>
    <xs:element ref="moment"/>
    <xs:element ref="momentabout"/>
  </xs:choice>
</xs:group>


</xs:schema>

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corresponding xml file is here:

<?xml version="1.0" encoding="UTF-8"?>
<document xmlns:CORE="http://www.reallysi.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:m="http://www.w3.org/1998/Math/MathML" xsi:noNamespaceSchemaLocation="oup.xsd">
<documentinfo publisher="OUPAustralia" title="Test Title - HE" titlenumber="1" isbn13="9780190311360" edition="4" author="Reynolds"/>
<chapter no="2">
<title><num>2</num><head>Inquiry Pedagogy</head></title>
<intro>
<para fo="Y"><txt><b>Good pedagogy</b></txt></para>
<para><txt><b>Research</b></txt></para>
</intro>
</document>

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Can anybody help me on this, why this error is occuring. Please provide me suggestion for this.